1. Field of the Invention
This invention relates to an apparatus for measuring biological information. More particularly, the invention relates to a biological measurement apparatus used to sensing and monitoring a specimen in an extracorporeal circuration, or to perform sensing and monitoring in vivo.
2. Description of the Prior Art
In clinical and medical fields, the continuous measurement and monitoring of ion concentration, gas concentration and the concentration of biological substances, especially enzymes, is desirable. Though an appreciation of continuous monitoring is growing in general medical treatment, a practical continuous monitoring system has not yet been realized. There are various reasons for this. One is that ion sensors and sensors for identifying biological substances do not operate stably in a living body or in biological solutions. Another is that ion sensors, gas sensors and enzyme sensors, which typically are glass electrodes, generally have a high impedence which renders them susceptible to adverse electrical effects. As a result, satisfactory monitoring circuits are not available. Moreover, when monitoring is performed over an extended period of time, variations of temperature affect measurement precision, thus making it difficult to achieve highly precise monitoring. Furthermore, owing to the influence of electrical disturbances, there is a limit upon how far apart the measurement section and processing section of the system can be separated from each other.